The present invention relates to a flexible print circuit board and more particularly to the holder plate for holding insulation films having a distributor section that comprises a cluster of printed conductive patterns.
FIGS. 5 and 6 respectively illustrate a plan view and a sectional view of a conventional flexible print circuit board typically used for a membrane switch, a doublet or a similar item.
In these drawings, reference numeral 2 and 31 respectively denote a flexible insulation film and a holder plate which rigidly hold the insulation film 2 by means of two-sided adhesive tape or some other bonding material not shown in the drawings. Portions 2a is not bonded to the holder plate 31, but projects from the holder plate 31, and constitutes a distributor section. Reference numeral 13 denotes a cluster of printed conductive patterns made of silver, carbon or other materials which is electrically connected with the wiring provided on the insulation film 2, but not shown in the drawings. Reference numeral 14 denotes a resist layer printed on a portion of the insulation film 2. The portion of the cluster of conductive patterns not covered by the resist layer 14 and exposed to atmosphere constitutes lead section 13a to be used for connection with external terminals.
Thus, electric signals in the wiring located on the insulation film 2 are conveyed by the cluster of conductive patterns 13 and taken from the lead section 13a.
A conventional, flexible print circuit board having an arrangement as described above is accompanied by a serious drawback. There, the cluster of conductive patterns 13 can be easily broken when the distributor section 2a is pressed hard against the juxtaposed edge of the holder plate 31 because the edge acts as a fulcrum of rotation.
The problem is serious, particularly with a flexible print circuit board designed for use with an electric appliance such as a washing machine or dryer. Because these appliances operate in a wet environment, the print circuit board is often equipped with a thick resist layer 14 or a plurality of resist layers 14 in an attempt to enhance the water proof and electric insulation of the board, thereby sacrificing flexibility. Hence, the board is very rigid.
When the distributor section 2a of such a flexible print circuit board is pressed against the corresponding edge of the holder plate 31 and bent, the resist layer 14, having a relatively poor flexibility, cannot follow the turning movement of the more flexible insulation film 2 and eventually comes off the latter. Then, part of the cluster of conductive patterns 13 may also be pulled off by the resist layer 14, thereby breaking some of the patterns.
Therefore, an object of the present design is to eliminate the above described drawback of the conventional technology by providing a flexible print circuit board which is highly resistant against bending deformations at the edge of the holder plate.